This invention relates to a Coriolis flowmeter that has a booster amplifier for increasing the power of the drive signals transmitted from a flowmeter electronics to a flowmeter sensor. More particularly, this invention relates to a booster amplifier which is operable with flowmeter sensors having flow tubes of straight and curved geometries, on numerous electrical voltage standards and under various environmental conditions.
It is known to use Coriolis mass flowmeters to measure mass flow and other information with respect to materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al., of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters typically comprise a flowmeter electronics portion and a flowmeter sensor portion. Flowmeter sensors have one or more flow tubes of a straight or curved configuration. Each flow tube configuration has a set of natural vibration modes, which may be of a simple bending, torsional, radial or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter sensor from a connected pipeline on the inlet side of the flowmeter sensor. The material is then directed through the flow tubes and exits the flowmeter sensor to a pipeline connected on the outlet side of the flowmeter sensor.
Flowmeter sensors typically include a driver for applying vibrational force to the flow tubes. The driver receives a drive signal from the flowmeter electronics and induces resonant vibration of the flow tubes. The frequency of the drive signals for a flowmeter sensor having a flow tube of a straight configuration can differ significantly from those of a flowmeter sensor having flow tubes of a curved configuration.
When there is no material flowing through a flowmeter sensor, all points along the flow tubes oscillate with a substantially identical phase. As material flows through the flow tubes, Coriolis accelerations cause points along the flow tubes to have a different phase. The phase on the inlet side of the flowmeter sensor lags the driver, while the phase on the outlet side of the flowmeter sensor leads the driver.
Flowmeter sensors typically include two pick-offs for producing sinusoidal signals representative of the motion of the flow tubes at different points along the flow tubes. A phase difference of the sinusoidal signals received from the pick-offs is calculated by the flowmeter electronics. The phase difference between the pick-off signals is proportional to the mass flow rate of the material flowing through the flowmeter sensor.
One of the pick-off signals is also used to form a drive signal control loop. The natural vibration modes of the vibrating, material filled system is defined in part by the combined mass of the flow tubes and the material within the flow tubes. Changes in the tube wall thickness, tube vibrational stiffness or mass of the material within the flow tube may require modified drive signals to induce resonant vibration. A drive control loop allows the flowmeter electronics to continuously generate drive signals that induce resonant vibration of the flow tubes.
Flowmeter sensors are typically sized according to a range of material flow rates appropriate for the flowmeter sensor. In order to increase the material flow rate, larger flow tubes may be utilized. Increases in flow tube size may increase certain flow tube parameters such as tube wall thickness and vibrational stiffness. The drive signal received from the flowmeter electronics may require additional power in order for the driver to induce resonant vibration of the larger flow tubes. A booster amplifier can be used to increase the power of the drive signals received from the flowmeter electronics.
A flowmeter sensor and a flowmeter electronics are typically interconnected by nine leads along a single path. Where the flowmeter electronics is remotely mounted from the flowmeter sensor, a 9-wire cable may be used. Where the flowmeter electronics is integrally mounted to the flowmeter sensor, a 9-pin feed-through may be used. Of the nine leads, two connect the flowmeter electronics to the driver, two connect the flowmeter electronics to one pick-off, two connect the flowmeter electronics to another pick-off, and three connect the flowmeter electronics to the temperature sensor. A booster amplifier is typically inserted along the single path interconnecting the flowmeter electronics and the flowmeter sensor.
It is a problem to design a booster amplifier that can operate on multiple AC voltage standards. Coriolis flowmeters are used worldwide. Individual countries and regions have standardized on certain electrical voltage levels. For example, the 115 volt AC standard is common throughout the United States, the 100 volt AC standard is common throughout Japan, and the 230 volt AC standard is common throughout Europe.
A traditional approach to designing booster amplifiers for Coriolis flowmeters has been to create separate booster amplifier models for each voltage standard. However as the matrix of booster amplifiers grows, the number of parts which must be specified, purchased and inventoried increases, manufacturing and labor costs increase through process complexity, and finished product inventories increase.
A further problem is designing a booster amplifier that is capable of amplifying drive signals for straight and curved flow tube geometries. The drive signals for a flowmeter sensor having flow tubes of a curved configuration can require a drive frequency approximating 40 Hz. The drive signal for a flowmeter sensor having a flow tube of a straight configuration can require a drive frequency approximating 800 Hz. As the frequency of the resonant vibration of the flow tubes increases, inaccuracies in the drive system become magnified resulting in mass flow measurement error.
A traditional approach to designing booster amplifiers for flow tubes requiring higher frequency drive signals has been to increase the power of the drive signal. However, power sources providing standard AC voltage may not enable sufficient power to be imparted to the drive signal. Examples of standard AC voltages are the 115 volt AC standard common throughout the United States, the 100 volt AC standard common throughout Japan, and the 230 volt AC standard common throughout Europe.
A further problem is designing a booster amplifier that meets regulatory agency safety standards for explosive environments. Coriolis flowmeters are used in various environments, ranging from inert to explosive. As the operating environment for the flowmeter becomes more severe, increasingly stringent requirements must be met by the flowmeter. Individual countries and regions have standardized flowmeter safety requirements through regulatory agencies. For example, UL determines flowmeter safety requirements in the United States, CENELEC determines flowmeter safety requirements in Europe, CSA determines flowmeter safety requirements in Canada and TIIS determines flowmeter safety requirements in Japan. A booster amplifier designed to meet an agency""s safety requirements for an explosive environment will typically meet that agency""s requirements for less severe environments. However, a booster amplifier meeting an agency""s safety requirements for an explosive environment may not meet another agency""s standards for an explosive environment. For purposes of this discussion, an explosive environment is an environment that includes a volatile material which can be ignited if a spark, excessive heat, or excessive energy is introduced to the environment.
One approach to meeting flowmeter safety requirements for an explosive environment is to encase the booster amplifier in an explosion proof housing. Methods used to achieve an explosion proof housing include encapsulation, pressurization and flame proof containment. An explosion proof housing prevents volatile material within the environment from contacting the device where heated surfaces of the device or sparks from circuitry in the device may cause an ignition of the volatile material. An explosion proof housing may also provide a flame path of sufficient length to cool any internal ignition prior to contact with volatile material external to the housing. Another approach to meeting flowmeter safety requirements for an explosive environment is to make the booster amplifier intrinsically safe. An intrinsically safe device is a device in which all of the circuitry in the device operate at certain low energy levels. By operating at low energy levels, the device cannot generate a spark or sufficient heat to cause an explosion.
A traditional approach to designing booster amplifiers for Coriolis flowmeters has been to create separate booster amplifier models for each operating environment subject to differing regulatory agency safety standards. However as the matrix of booster amplifiers grows, the number of parts which must be specified, purchased and inventoried increases, manufacturing and labor costs increase through process complexity, and finished product inventories increase.
A further problem is designing a booster amplifier that meets regulatory agency safety standards for explosive environments which is easy to service and install. A booster amplifier designed to meet regulatory agency safety standards for explosive environments can include complex installation and service requirements. Booster amplifiers can include an installation requirement for a separate earth ground and assemblies which must be replaced upon service of the booster amplifier in order to meet flowmeter safety requirements for explosive environments.
A booster amplifier strictly includes all of the conductors, circuitry and housing necessary to receive the drive signal from a flowmeter electronics, amplify the drive signal, and send the drive signal to the flowmeter sensor. However, flowmeter electronics typically send to and receive from the flowmeter sensor all signals necessary in the operation of the flowmeter through a single path. Therefore for purposes of this discussion, a booster amplifier may also include all of the conductors and housing necessary for sending to and receiving from the flowmeter sensor additional signals where the path from the flowmeter electronics used for the drive signal includes additional signals.
The above and other problems are solved and an advance in the art is made by a booster amplifier provided in accordance with this invention. A first advantage of this invention is that the booster amplifier can operate with a plurality of electrical voltages. A second advantage of this invention is the capability of the booster amplifier to amplify drive signals for straight and curved flow tube geometries. A third advantage of this invention is that the booster amplifier meets numerous regulatory agency safety standards for explosive environments. A fourth advantage of this invention is ease of service and installation of the booster amplifier.
The booster amplifier provided in accordance with the present invention is operable with a plurality of different standard voltages through the use of offline switching power circuitry. Examples of standard voltages are the 115 volt AC common throughout the United States, the 100 volt AC common throughout Japan, and the 230 volt AC common throughout Europe. Offline switching power circuitry receives an AC voltage from a power source, rectifies the AC voltage to a corresponding DC voltage and converts the corresponding DC voltage to a single uniform DC voltage. The drive circuitry operates on the single uniform DC voltage output by the offline switching power circuitry.
The booster amplifier provided in accordance with the present invention amplifies the drive signals for straight and curved flow tube geometries. The drive signals for a flowmeter sensor having flow tubes of a curved configuration can require a drive frequency approximating 40 Hz. The drive signal for a flowmeter sensor having a flow tube of a straight configuration can require a drive frequency approximating 800 Hz. As the frequency of the resonant vibration of the flow tubes increases, the phase of the drive signal must be more precise in order to efficiently induce resonant vibration of the flow tubes. Phase shift circuitry modifies the phase of the drive signal received from the flowmeter electronics to efficiently induce resonant vibration of the flow tubes.
The booster amplifier provided in accordance with the present invention meets numerous regulatory agency safety standards for explosive environments. Examples of regulatory agencies setting flowmeter safety requirements for explosive environments are UL in the United States, CENELEC in Europe, CSA in Canada and TIIS in Japan. The booster amplifier provided in accordance with the present invention meets regulatory safety standards for explosive environments through the use of barrier circuitry and environmentally innocuous housing. Environmentally innocuous housing uses a plurality of explosion proof housing techniques in order to meet regulatory safety standards for explosive environments, including explosion proof encasement and flame path containment.
In order to amplify the drive signal received from the flowmeter electronics, the booster amplifier utilizes power in excess of the intrinsically safe threshold. The housing for the portions of the booster amplifier having non-intrinsically safe conductors or circuitry utilize explosion proof encasement techniques to meet regulatory safety standards for explosive environments.
In order to avoid using explosion proof encasement techniques for the entire booster amplifier, the portions of the booster amplifier having non-intrinsically safe conductors or circuitry are isolated from the remainder of the booster amplifier. Barrier circuitry isolates the non-intrinsically safe conductors and circuitry from intrinsically safe circuitry or conductors. Barrier circuitry prevents the power in excess of the intrinsically safe threshold from being transferred from the non-intrinsically safe circuitry to the drive signal received from the flowmeter electronics during operation of the booster amplifier and in the event of a short. The housing for the barrier protected intrinsically safe conductors adjacent to the portion of the booster amplifier containing non-intrinsically safe circuitry or conductors utilize flame path containment techniques to meet regulatory agency standards for explosive environments. Flame path containment techniques provide a flame path of sufficient length to cool any internal ignition prior to contact with volatile material external to the housing.
Environmentally innocuous housing may include an interface housing component, a drive circuitry housing component, and an amplified drive signal conduit component. However, flowmeter electronics typically send to and receive from the flowmeter sensor all signals necessary in the operation of the flowmeter through a single path. Therefore, the environmentally innocuous housing may also include a non-drive signal conduit component. The non-drive signal conduit component provides housing from the interface housing component to the flowmeter sensor for any additional signals received over the path which included the drive signal.
The interface housing component receives the drive signal from the flowmeter electronics. The interface housing component serves as a junction for the drive and other signals received over the path which included the drive signal, as a mounting bracket for the booster amplifier, and as a receptacle for the terminus of the flowmeter electronics. The interface housing component provides a flame path between the interface housing component and the drive circuitry housing component. The interface housing component utilizes flame path containment techniques to meet regulatory agency standards for explosive environments.
The drive circuitry housing component houses the barrier circuitry, the phase shift circuitry, the offline switching power circuitry, and the drive circuitry. The drive circuitry housing component is connected to the interface housing component and the amplified drive signal conduit component. The drive circuitry housing component receives the drive signal from the interface housing component and a standard voltage from the customer supplied power source. The circuitry and conductors housed within the drive circuitry housing component may exceed the intrinsically safe threshold. The drive circuitry housing component utilizes explosion proof encasement techniques meeting regulatory agency standards for explosive environments.
The amplified drive signal conduit component houses the amplified drive signal. The amplified drive signal conduit component is connected to the drive circuitry housing component and the flowmeter sensor. The circuitry and conductors housed within the amplified drive signal conduit component may exceed the intrinsically safe threshold. The amplified drive signal conduit component utilizes explosion proof encasement techniques meeting regulatory agency standards for explosive environments.
Flowmeter electronics typically send to and receive from the flowmeter sensor all signals necessary in the operation of the flowmeter through a single path. Therefore, the environmentally innocuous housing may also include a non-drive signal conduit component. The non-drive signal conduit component provides housing from the interface housing component to the flowmeter sensor for any additional signals received over the path which included the drive signal. As the non-drive signal conduit component does not contain non-intrinsically safe conductors or circuitry and is not adjacent housing containing non-intrinsically safe conductors or circuitry, explosion proof housing techniques are not necessary in order to meet regulatory agency standards for explosive environments.
The booster amplifier provided in accordance with the present invention increases ease of service and installation. Barrier circuitry may comprise galvanic isolation device circuitry (GID). The GID eliminates the need for a separate earth ground for the barrier circuitry. The elimination of a separate earth ground reduces cost and increases ease of use and installation for the customer. The amplified drive signal conduit component may include first and second connector members and a conduit member allowing disassembly and reuse of the amplified drive signal conduit component. Disassembly and reuse of the amplified drive signal conduit component increases ease with which the booster amplifier can be serviced.